First of all let me say that this does NOT sound like cancer at all...it sounds like hemmeroids. Those suckers can bleed but pose no threat beyond inconvenience.
What I say next may scare you but keep reading and I will talk you down from the edge.
My father in law (age 70) has colon cancer. He never had any bleeding , but he did have bouts of both severe diahrea and severe constipation. He is now in chemo and doing very well.
At your age (and I mean that clinically) hemmeroids are common. I would ask your GI doc about this and chances are all you will need is some preparation H and you will be fine. In addition adding more fiber to your diet or usind a fiber supplement like metamucil may help. Note: increased fiber can cause thin stools or mild diarrhea so don't freak out if this happens.
If all your tests came back negative then you are fine. You just need to start believing it even if that is easier said than done. Hang in there!